An X-ray detector is an apparatus, for example one used for EDX (Energy Dispersive X-ray Spectroscopy), used for qualitative analysis such as for examining the compositional analysis of a sample.
When an electron collides with the sample, various kinds of electrons, ions, characteristic X-rays, etc., are emitted. An X-ray detector, such as an EDX, detects the emitted characteristic X-rays and expresses them according to the energy band of a beam. The characteristic X-rays have a magnitude that is energy-specific for each material. Therefore, a computer analyzes the material by comparing the magnitude of energy with pre-stored values of the magnitudes of energies for various materials.
These days, X-ray detectors and scanning electron microscopes are frequently used together. A scanning electron microscope may be used to perform a structural analysis of a sample. The scanning electron microscope scans electrons to perform this structural analysis. X-rays are generated by collision of the scanning electrons on the sample. These X-rays may be collimated by an X-ray detector. Therefore, when the scanning electron microscope and the X-ray detector are combined, structural analysis and compositional analysis may be performed at the same time.
FIG. 1A is a schematic diagram of a conventional EDX. Referring to FIG. 1A, a conventional EDX includes a cryo compressor 101, a filter 103, an isolation block 105, a cooler head 107, a manual valve 109, an electrical isolator 111, a main chamber 113, an X-ray detector 100, an I/O panel 115, and an EDX rack 117. Among the components of the conventional EDX, the X-ray detector 100 will be described hereinafter, with reference to FIG. 1B.
FIG. 1B shows a typical structure of a conventional X-ray detector 100. As shown in FIG. 1B, the conventional X-ray detector includes an X-ray collimator 120 for collimating the X-ray, an electron trap 130 for eliminating electrons from the collimated X-ray, a window 140 for transmitting the X-ray and sealing an interior of the X-ray detector so as to vacuumize the interior of the X-ray detector 100, a crystal 150 for generating an electric current corresponding to the energy of the X-ray, and a field effect transistor (FET) 160 for generating a voltage signal corresponding to the electric current generated by the crystal 150.
Since the crystal 150 and the FET (which are main parts of the X-ray detector) produce substantial noise at high temperatures, the crystal 150 and the FET are cooled to reduce the noise, and the X-ray detector 100 is sealed and maintained in a vacuum state. A vacuum is created within the interior of the X-ray detector to prevent contamination therein, oxidation of a filament, electric discharge, etc.
The noise produced by the crystal 150 decreases as the temperature thereof becomes lower. However, the noise of the FET only decreases until a certain temperature is reached; then, as the temperature becomes excessively low, the noise associated with the FET rises again. Therefore, an appropriate temperature must be maintained by a heater. Although not shown in the accompanying drawings, a heater is provided in the X-ray detector and is controlled by an external control module.
The inside of the X-ray detector 100 is cooled by liquid nitrogen (LN2). To this end, a cryostat 200 is provided. The cryostat 200 is connected to an X-ray detecting device including the X-ray detector 100.
The liquid nitrogen is contained in the cryostat 200 and is usually consumed at a rate of about 1.1–1.3 liters a day.
Therefore, liquid nitrogen is periodically supplemented from a liquid nitrogen tank 300. The liquid nitrogen supplemented from the liquid nitrogen tank 300 to the cryostat 200 passes through a filter to prevent the inflow of foreign particles.
As described above, since the conventional X-ray detector 100 is used while being connected to the cryostat 200, various inconveniences including the periodic or aperiodic supplement of the liquid nitrogen and replacement of the filter occur.
In addition, since these are consumables, the maintenance cost is increased.